Saturday, November 30, 2019

Stern tube Leakage Test

  • Oil to be used must not attack sealing Rings. Generally oil used for main propulsion unit is SAE 30. Remove screw plug and fill up the stern tube oil. Oil pressure must amount to only 0.2 – 0.3 Kg/cm² more than SW pressure. 
  • Preheated to 60 – 70°C when viscose oil is used or low temperature prevails. 
  • Remain in this condition for several hours (says overnight) and turn engine by Turning Gear to change the shaft position 3 – 4 times. 
  • Check oil leakage from Drain Plug and if it is all right, fit back Drain Plug and fill oil from venting and Filling Plug and close. 
  • Forward Seal is fitted.


How do you test a fresh water generator plant for leaks?

  • Close the outlet of the distillate pump, vacuum breaker valve, bottom blow off valve and feed water valve
  • Inject air into the evaporator shell 
  • Keep the shell pressed up to about 1.0bar gauge 
  • Sprinkle soap solution on to the jointings, packings, and suspected areas of the shell

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Steering gear motor safeties

  • Overload alarm. 
  • 200% insulation in motor. 
  • High temperature alarm.
  • Self-starting after power failure. 
  • Short circuit trip.
  • Phase failure alarm.
  • One of the steering motor is fed from the emergency bus. Hydraulic side there is two trips  a. Low level cutout b. High lube oil temperature cutout. 


Windlass safeties

  •  Electromagnetic brake.
  •  Motor overload protection.
  • Short circuit protection.
  •  Restart delay timer.
  •  A Restart stop. 
  • Manual brake / mech. Brake.
  • Cable stopper.
  • Slipping clutch (torque limiter).
  • Relief valve


Ovality of auxiliary engine crank pin

  • Combined effect of reduced effectiveness of L.O and directional thrust of the con rod. This is maximum at around 45 degree ATDC Uneven loading of units and overloading 
  • Max Allowed: 1/4th of the bearing clearance  Removed By: Insitu Grinding and polishing  
  • Reference: Fillet of crank web Max. Allowed Grinding: 2mm, because after grinding 2mm or more surface hardness reduces drastically. Due to this maximum allowable grinding is 2mm. Bottom bearing damage reason is the ovality, bearing clearance and condition of L.O supply


Uniflow scavenging advantages

  • Better scavenging for cheaper fuel.
  • No exhaust and scavenging mixing.
  • Working temperature reduces.
  • Cylinder lub oil consumption less.
  • Less radial exhaust remains after scavenging
  • Air loss during scavenging and exhaust nil
  • Thermal stress less
  • Liner design simple


Ultra Low Sulpur Diesel (ULSD) problems

  • ULSD contains low level of lubricity.
  • Natural lubricity is provided by oxygen and nitrogen compounds aromatics ,hydrocarbons and sulphur.
  • Refining process reduces these chemicals.
  • Engine and fuel oil system rely heavily on lubricity for proper operation.
  • Insufficient lubricity leads to premature failure of wear related fuel system components including fuel pump and injector.
  • ULSD is hygroscopic fuel .This means it absorbs water from atmosphere 
  • Water weaks havac in diesel fuel system causing corrosion and failure of metal componets such as fuel tanks, pumps and injectors .
  • Water leads to microbial contamination which results in plugged fuel lines and filters
  • In cold climate water freezes resulting in reduced power and total engine shutdown.


Oblique cut on conrod of Aux engine

  • To reduce size of the engine.
  • To reduce crankpin dia.
  • If not oblique cut not able to lift same from top with piston.
  • If not oblique cut have palm bolts ,increase in production cost.
  •  Apart from this , as engines are becoming more efficient the liner bore dia is not increasing but as the power output is increasing the bottom end bearing size is increasing , because it has to transmit so much of the peak pressure (downward thrust) .Because the thrust is increasing the bottom end bearing size has to increase , liner dia and bore remains almost same.